Multiple-focus x-ray tube



Aug. 13 1 935.

.1. F. LEE

MULTIPLE FOCUS X-RAY TUBE Filed D60. 4, 1934 JAMES F LEE INVENTOR ATTORNEY Patented Aug. 13, 1935 MULTIPLE-FOCUS X-RAY TUBE James F. Lee, PaloAlto, Calif.

, Application December 4 1934, semi-m. 755,874

10 Claims. (erase-35) inventionrel'ate's tomultiple-iocus X-ray tubes and its primary object. is .toprovide an effective safeguard against mistakes by the technician with respect to the focal spot setting.v further object'is to facilitate initial adjustments of the several focal spot areas during the course of manufacture so that all tubes of a given designationwill have identical focal-spots.

'Ifhere' are two general types of multiple-focus XrayIWubes, .namelyi the single filament and double'filament types, respectively. The present invention is. applicable to and is herein described with reference to both those types of tubes.

Both possess v great advantage] over single-focus tubes; but their" commercial success has, in. the past, been somewhat hampered bytheir greater siiscepiiibi:lity to mistakes on the part of the technician with respect to the focal-spot settings-a single mistake of that character sometimes being enoughto destroy the usefulness of a costly tube.

X -ray technicians are, as a rule, intelligent and alert people and when one makes a mistake as t() aiocal-spot adjustment it is not due to carelessness but to iaulty memory or confusion. Hence if some meansbe provided, as is here done, which will inform the technician clearly and unmistakably as tothe adjustment of the tube, it is. tobe-expected that errors of the kind here dealt withwillbecome exceedingly rare. With an X-ray tube equipped according to the present invention, adjustment of the focal-spot area is efiectedby means of a key which must be inserted in a keyhole provided in the tube in order to obtain a focal-spot smaller than the largest spot which the tube is designed to produce. For a two-focustube only ne key would beneeded; but for tubes intended to operate on a larger number of focal-spotareas, a proportionately larger number of keys are required. The four-focus tube here selected for illustration requires three keys. v Each key, preferably, is pro- .vided with a.- large head or flag bearing some suitable notation such as a large numeral and, pref as, in fact, it is not. 7 Likewise, only gross negligence or irresponsibility could account for fail ure to distinguish between the different'keys. The present application emphasizesmore'particularly'the single filament type of multiplefocus' X-ray tube, which is' usually designed to provide four focal-spot. settings; and the mechanism herein illustrated and described (except that of Fig. 12) is intended to. be embodied inan X-ray tube such. as that described and claimed in the. co-pending application of James FJLe, Serial Number 721,142, filed April 18, 19 34',-' to which reference is here made for a'description of the focus-adjusting mechanism.

In the fication: t r;

Fig- 1 is an elevational View, partlyin section, of the end portion'of the cathode arm of a single filament. multiple-focus tube illustrating, inter alia', the screw plug for making electrical 'connections, the re-entrant stem which forms a'support for the cathode and iocus-adjustingmechanism, the operating lever by means of which the focus-adjusting mechanism is manipul'atedand the head or. flag of one of the keys which function to operate the focus-adjusting mechanism a and to apprise the operator of the focal-spot setting; 7

Fig. 2 is across-sectional view taken along "the line 2-2 of Fig. 1; FigflQB isa view taken along the line 3-13 of Fig. 1 showing the key operated mechanism with a key inserted; Fig. 4 is'an' endwise view of the tube; I, "Fig. 5'is an enlarged cross-sectional view taken along the line 5 -5 of Fig. 3;

Fig. 6 is a. longitudinal sectional view along, the line' 6 f'6 'of Fig/3'? "Fig.1 is a fragmentary view taken line 1- -1 '01 Figs.1and'3; g I

Figs. 8, 9 and 10 are side-elevational' viewsof three keys, each of which is designed to operate the focus-adjusting mechanism to bringabouta certain predetermined focal-spot adjustment; I

Fig]. 11 is a cross sectionalview along the linens |IIl of Fig. 8; and v Fig. 12 is, a combined structural and diagramjmatic illustration of the manner of "applying the present invention .to a two-filament twofocus X-ray tube. j A complete multiple-focus X-ray tube of the single filament type comprises, as its principal constituents; an evacuated glass envelopeenclosing an anode or target together withan electron-emissive cathode, an adjustableiocusl6 magma PATENT OFF E") drawing which accompanies 'thislspeci- [5 taken, 1, l

ing shield or shields and a focus-adjusting mechanism operable to bring about suitable relative movements between the cathode and the focusing shield or shields whereby the size of the focal-spot is rendered variable at the will of the operator. The manner of operation of high vacuum hot cathode X-ray tubes, of which genus the tube ofthe present invention is a species, is

- too wellknown to require explanation here; and

the focus-adjusting mechanism intended to be utilized in conjunction with'the present invention is'fully described in the previously identified Lee application. It is, therefore, considered unnecessary in the present case to illustrate and describe an entire X-ray tube or an entire focus-adjusting mechanism. Hence, all that is shown in the drawing is a portion of the cathode arm structure and a portion of thefocus-ad- V justing mechanism including the key-operated device through which the focus adjusting mechanism is manipulated and controlled and [w ich constitutes the subject matter of this nvention. V v 7 Q The showing of Fig. 1 is of a'portion of, the cathodearnnso c'alled that is, of the cathode ,end of anX-ray tube which,.in a bulb type tube would be an arm. Many X-ray tubes nowadays .h avefno bulbous mid-portion and therefore, ac-

curately speaking, no cathode arm. That term,

the focus-adjusting ,rnechanism size of, the focal-spot.

however, iswell understood in the artand is convenient to .define that portion of the tube which includes the cathode jand cathode terminal' contacts even though theitube may be of the straight cylindrical type having no bulbous portion. If that term is usedhereafter in this specification or any of the" appended claims its broader significance is intended.

-j 'I hejevacuated cylindrical glass envelope I3 has a tubular glass re-entrant stem M which is integral with the envelope. To the right hand end of envelope {3 is secured 'arnetal cap consisting ofa tubular sleeve l5 and a screw threaded con-- ,end-or lip of the re-entrant stem: "This dia-.

,phragm serves as a vacuum-tight medium, for the transmission of mechanical motion from the exterior ,tothe evacuated interior of the envelope whereby theoperator is enabled to manipulate so as to vary the "The cathode head comprises, in diaphragm suitable focusing elements or shields and a foaddition to ou sadjusting mechanism includinga metal tube ,JBJa nd tubular glass extension l9, which mechco-pending application.

lan'iismjis" capableof translating the simple motion of an operating lever into appropriate movements of the focusing elements-all of which is fully described in applicant's above-identified Inasmuch as the cathode head structure of the.present caseis identical with that of the aforementioned co-pending' application, it is ,consi der'e dunnecessary. to repeat the disclosure here beyond showing enough of the structure to fully illustrate the manner of applying the present invention. I -.,.;A. 2 ;2 aind .ieepelisantf .sfir sns e Pa e I1, an felectron-emissive cathode,

the metal tube I8 is secured by welding or otherwise to the diaphragm ll, through the radial center of which it extends, and this tube functions as an operating lever havingits pivotal point or fulcrum at the point of juncture' with the diaphragm. The flexibility of the diaphragmbeing drawn to a point and sealed 01f aftercompletion of the pumping operation as indicated at obscured the showing of retracting spring 2|.

Viewed endwise, as per Fig. 3, the free end of the operating lever (tube l9) traverses an arouand it is engaged by a loop formed in member 20 which is pivoted at26 and provided with a cam followerin the form of a roller 22 whichiis adapted to be actuated by a key whenthe |9a in Fig. 1. In Fig. 6 tube-l9 is not shown] 1 sealed ofi because to have done so would have ate path indicated bythe dot and dash. line latter is inserted in the key g uide-23 as "shown in Fig. 3.

Key guide 23is madeof a piecefofinetal tub} I ing slotted on one side and out backtof provide clearance for roller 22 and the enlarged loop portion of member 20 intheir respective'retract- .ed positions. Member 2lllis engaged by a hair pin type wire retracting spring 2| which is secured atone end to sleeve l5. I

An annular'plate 2,1 is fastened inside sleeve l5 and forms a support for pivot 26; and the tubularkey guide 23 is brazedor otherwise Se-.

cured at its ends to thejinside surface'of sleeve Fig. '7 shows the keyhole as'viewed from the exterior of the tube and Figs. 8, 9 and '10 are side elevational views of three keys, each'of which corresponds to a different focal spot Fsetting. The keyshown in Fig. 8 is thatof Fig. 3-and is the one which affords the maximum movement of the operating lever and consequently the smallest focal-spot. This'is ordinarily the number l-key-. The other two keys, Figs. 9-and 10, respectively, afford successively smaller "movements-F01" the operating lever and they correspond to two ii termediate sized focal-spots. The latter keys should bear notations f2 and 3 respectivelyiforidentificatior1--those being the numbers commonly four-focus tube. i a p v Y b With no key inserted the en'dof the operating lever is held by spring 2| in its furthermcst right assigned to theintermediate focal spots iri'a hand position (as viewedin Fig. -3)which' positioncorresponds to the broadest focal spot; Fig. i

3 has been drawn withthe numberjlfkey inserted and'the operating leveris thereforeshown 'inf-its 'furthermost left hand position.

' It will be apparent that with no key inserted the tube isalways adjusted torne'et its maximum rating and no damagewillbe done as theresult of a technicians faulty memorye-whi'ch would be [likely to happen if the tube did not automatically restore itself to the broadest focal spot setting upon the withdrawal'ofa key. If thetube is ad.

justed forany of thesmaller focal-spots one of the keys is necessarily in place and there is no excuse whatever for a technician making a mistake as to the focal-s'pot setting'because itsnum ber stands out boldly;.on'. the head of the key.

- M mbe .se e n em P? ma el r mf .long metal strip bent as shown in Fig. 3. See also the enlarged ,crossesectional view, Fig. 5. f extension a is designed to engage key guide 23 and act as. an adjustable stop. By bending this extension the area of the broad focal-spotcan be adjusted. This is done in the course ofmanufac- -ture of the'tube; but such an adjustment canalso ."be made afterward if need be.

The

. The devicewhich hasibeen describedis notonly well adapted to fulfill its primary function which is toprevent mistakes as. tofocal-spot settings,

but it offers a very substantial advantage in that --it permits of asimple and easily performed initial determination of the focal-spot areas during manufacture of the tube so as to take care of unavoidable manufacturing variations. All tubes .of., aparticular designation must have idential focal-,-spots; otherwise individual rating charts wouldhave tobeprepared and supplied with each au- MB intolerable condition. With the arrangement described= any: deviation from standard in v the area of the broad focal-spot can be corrected by adjusting the extension 200. and similar deviations from standard in the other focal-spot sizes can be corrected by cutting the cam surfaces of the keys to allow for the errors noted.

It will be obvious that an increased number of focal-spot sizes can be provided for by increasing the number of keys and that the sizes of the focal-spots can be whatever is specified between the maximum and minimum limits of the tube.

Fig. 12 illustrates how the key-operated safety provision can be applied to a two-filament X-ray tube. 1 Here a pivoted switch blade or contact arm 31 is substituted inplace of member 20. This is provided with a cam follower 28 which engages a key 29. The two filamentary cathodes are indicated by reference numerals 30 and 3|; and

conductors 32 and 33 lead to the filament current source. With the key inserted as shown, contact arm 31 engages contact spring 34 and a circuit is completed through cathode 30. When the key is withdrawn contact arm 31 is moved by its retracting spring 35 out of engagement with contact spring 34 and into engagement with contact spring 36. This completes a circuit through cathode 3|. The key, is, of course provided with a large head or flag bearingan appropriate notation as in the previous case.' If cathode 3| is the one corresponding tothe broad focal-spot, it follows that the tube is alwaysset for the broad focal-spot when the key is withdrawn.

What is claimed is: I

1. The combination in a multiple-focus X-ray tube of focal-spot adjusting means including a keyfor, said device being operable automatically,

when not influenced bysaid key, to cause the X- ray tube to be adjusted to produce a relatively broad focal-spot and to hold'the tube in that adjustment, said key being operable to actuate said device and thereby cause the X-ray tube to be adjusted to produce a relatively fine focal-spot,

said key having a head of substantial size which is adapted to be observed by the operator when 'lthe-key'is in use, said head having avisible indicate tor corresponding; to the focal-spot. adjustment ofythe tube.

3.; The combination in. a'multiplefocus Xeray 'tube of focal-spot adjusting means includingi'za key-operateddeviceandian operating key there'- for, said device comprising a pivoted member, 1 which is rotatable about its pivot, and .a spring operable, whenever said member is not influenced by said key, to move said member into a position whereinit causes the X-ray tube ,tobe adjusted to produce a relatively broad focal-spot and to hold the tubein thatadjustment, said key being operable to actuate said pivoted member and thereby cause the X-ray tube to be a-djusted to produce a relatively fine focal-spot.

- :4. The combination in a multiple-focus X-ray tube having an evacuated envelope, of focal-spot adjusting means including an operating lever extending from the evacuated interior of said envelope to the exterior thereof, a spring. operable to actuate said operating lever and. to'yieldably; hold envelope to the exterior thereof a spring operable to actuate said operating lever and to yieldably hold said lever in a position corresponding to the broadest focal-spot adjustment of the tube, a keyguide adjacent said lever, and a key operable, when inserted into said key-guide, to move said'lever out of the aforementioned broad focal-spot position against the action of said spring into another position corresponding to a finer focal-spot adjustment. 7

6. The combination in a multiple-focus X-ray tube having an evacuated envelope, of focal-spot adjusting means including an operating lever extending from the evacuated interior of said envelope to the exterior thereof, a pivoted member engaging said operating lever, a spring operable to move said member and operating lever about the fulcrum of said pivoted member to one extreme position corresponding to arelatively broad focalspot setting of the tube, a'key-guide adjacent said member and a key, operable, when inserted into said key-guide, to move said member together with said operating lever against said spring into another position corresponding to a finer focalspot adjustment.

'7. The combination in a multiple-focus X-ray tube having an evacuated envelope, of focal-spot adjusting means including an operating lever extending from the evacuated interior of said envelope to the exteriorthereof, a sleeve carried by said envelope adjacent the exterior free end of said oprating lever, a pivoted member carried by said sleeve and engaging said operating lever, a spring carried by said sleeve and arranged to press upon said member, thereby'normally causing said operating lever to be yieldably held in a position corresponding to the broadest focal-spot the tube is designed to produce, a key-guide 'carried by said sleeve adjacent said member and having an opening to permit protrusion of a key therefrom into engagement with said member, and a key adapted to be inserted into said key-guide and, when so inserted, to move said member about its pivot together with said operating lever against the opposing pressure of said springinto a'position corresponding to a finer focal-spot adjust ment, said key having ahead of substantial size which is adapted to be observed -by the operator when the key is in use, said key-head bearing a visible notation corresponding to the focal-spot I adjustment of the tube.. 1

8. The combinationuwith a multiple-focus-X- .raytubehaving means susceptible to manual control for: varyingthe area of the focal-spot,- of a key operable upon said meansto efiect variation of the :foeal-spot area, said key being-separable from the tube and having a head of substantial size :which is adapted to be observed by the operator 7 when the key is in use, saidhead bearing avisible notationcorresponding to the focal-spot adjusti'ment ofthetuba. a

.9. Thelcombination with a multiple-focus X- ray tube having mea'nssusceptible to manual con- :trol-for varying the area of the focal-spot, of a Lplurality of keys operable individually upon said use said key-heads each'bearing an individual =5;

visible {notation correspondingv to a particular focal-spot adjustmenheach of said keys being designed to adjust the focal-spot to a predetermined areaiwhich differs from that-of each of the others of said keys.v e v..-

10. The combination in a-multiple-focus X- ray tube having a plurality of cathodes each'olf ferent area respectively, of a key-operated device for selectively closing a circuit through said cathodes individually, said device including a which is adapted to produce a focal-spotot difswitch member having aplurality of" operating positions in each of which it closes a circuit key operable to move'said switch member from one of its operating positions'to another.

- JAMES through one of said cathodes individually,"and a a 

